Drill collar clamp



June 5, 1962 A. R. sToKEs 3,037,258

DRILL COLLAR CLAMP Filed June 23. 1960 4 sheetsfsheet 2 F/GZ ATTORNEY June 5, 1962 A. R. sToKl-:s

DRILL COLLAR CLAMP 4 Sheets-Sheet 3 Filed June 23, 1960 7 rl@ F ALV/N RSTOKES INVENTOR.

AT TO F NEY June 5, 1962 A. R. sroKEs DRILL COLLAR CLAMP 4 Sheets-Sheet 4 Filed June 25, 1960 FIG. /O

F/Gl/ A LV/N RSTOKES INVENTOR.

BY Il A TTO R N E Y 3,037,258 Patented VJune 5, 1962 nnte 3,037,258 DRILL COLLAR CLAMP Alvin Ray Stokes, 3131A. Coolidge St., Borger, Tex., assignor of lfty percent to Jimmie Blanks, Borger, Tex. Filed June 23, 1960, Ser. No. 38,146 8 Claims. (Cl. 24-249) This invention has to do with well drilling tools and has particular reference to an improved clamp. This clamp is of particular use to prevent the dropping of cylindrical tools such as drill pipe, drill collars, and the like during their manipulation at a rotary table.

In drilling wells by the rotary method, power to rotate the drill bit is transmitted from the power source at the surface to the bit by means of pipe known as drill pipe. Such drill pipe is made in lengths of 20 to 4() feet. As the well is drilled deeper, joints or lengths of such pipe are added to the string already in the drill hole and the drilling is thus continued at greater depth as the pipe works its way downwards. The drilling bit, in normal usage, becomes worn to a point at which such must be replaced. Thereupon, the whole drill string is withdrawn, the bit is replaced and the components of the drill string then are assembled, length by length, and lowered into the well with the new bit attached thereto. Withdrawing and installing drill strings thus necessitates several operations and manipulations of the separate joints or lengths and their associated collars, whereby the entire drill string is supported in the hole on slips in the rotary table while further joints or strands are removed from or added to the string thus supported. This repeated sequence of movement of the drill string, holding the string and removal and replacement of the lengths of pipe forming the drill string, while supporting the drill pipe is a difficult, physically tiring operation. It is also nerve-wracking as it involves the employment of substantial manpower on the rig and there are substantial hazards of accident to personnel and equipment.

In these manipulations of the drill string and the component thereof for running in and removing drill strings, production strings, etc., slips provided in the rotary table for support of the drill strings during these operations frequently fail to obtain an effective grip on the string which they are purposed to support. Such failure may allow the pipe, liner, or other object being supported to fall into the well, necessitating expensive time-consuming fishing operations for its recovery as well as endangering personnel by the falling of such heavy equipment.

According to this invention, there is provided a clamp adapted for such circumstances of repeated cycles of attaching and clamping on such pipe for only short intervals followed by release of such pipe, i.e., a device for quickly clamping and subsequently quickly releasing such clamp.

A general object of this invention is to provide a convenient as well as practical, effective, and dependable clamp.

Another object of this invention is to provide an improved clamp that may be conveniently, quickly, and controllably engaged about the pipe, drill collar or other object, at a point above the rotary table and which clamp is adapted to reliably and controllably engage down against the slips or other parts at the rotary table to prevent the falling of the pipe or similar object in the event the rotary table slips fail to support the pipe or similar object.

Another object of this invention is to provide a clamp of the above characteristics that is also operable to quickly and conveniently and controllably obtain a dependable, positive grip on the pipe, drill collar, liner, or the like, even when such presents a smooth surface devoid of shoulder, collars and recesses.

Yet another object of this invention is to provide a clamp of the above characteristics that may be easily and quickly adjusted in effective diameter to adapt it for use with a wide range of sizes of pipe and the like.

The above and other objects and advantages of the invention will be apparent during the course of the following description of the invention, throughout which description reference is made to the accompanying drawings which form a part of the description, wherein like numerals are employed to designate like parts, and in which:

FIGURE 1 is a plan view of a preferred embodiment of the invention in operative position about a drill pipe, such pipe being shown in section;

FIGURE 2 is a diagrammatic side elevational viewrof the clamp of the invention in operative position on a pipe supported in the slips of a rotary table;

FIGURE 3 is a diagrammatic side view of the handle assembly 69 of the invention as seen along direction indicated by arrow III of FIGURE l;

FIGURE 4 is a diagrammatic side View of the arm 71 as seen along the direction indicated by arrow IV of FIGURES l and 2;

FIGURE 5 is a cross-sectional View takenI along the plane V'V" of FIGURE 4;

FIGURE 6 is a side view of t-he jack body 89' as seen along the line indicated by arrow Vl of FIGURE 1;

FIGURE 7 is a diagrammatic partly sectional view of jack FIGURE 8 is a diagrammatic sectional view through intermediate link 25A, along plane VlIIL-VIIP of FIG- URE l0;

FIGURE 9 is a perspective view of intermediate link 25A;

FIGURE l0 is a front View of intermediate link 25A; and

FIGURE 1l is a diagrammatic perspective representation of the mechanism for holding handle 111.

The clamp made according to the present invention, shown generally as 29, comprises a plurality of like intermediate pivotally connected links, 25A, 25B, 25C, 25D, 25E, ZSF, ZSG, 25H, 251, and 25], in a link assembly 21 and means 22 for releasably and conveniently connecting the ends of the link assembly 21 to hold it engaged about a pipe, collar or other generally cylindrical item 23. The like intermediate elements of the link assembly 21 are generally shown in U.S. Patent 2,301,625. The clamp of this invention forms a substantially annular structure for fitting about a pipe or cylindrical object 23. In accordance with this invention, such may be readily varied as to its length or diameter to lit pipe and like objects varying greatly in diameter. rThe intermediate links, 25A-25l, are preferably identical. The number of such links employed depends on the size of the pipe being handled as described in U.S. Patent 2,301,- 625, page 3, left column, lines 42-57. At one side of body 29 each intermediate link, as 25A, has a horizontally projecting annular lug or eye 30 that is provided with a vertical cylindrical opening 31. At the other side of each intermediate link body, as 29, is a horizontally projecting fork 32 comprising two vertically spaced annular ears or lugs, 33 and 35, adapted to receive the eyes as 30, of adjacent links, as 25B, and having vertical openings 37 for registering with opening (corresponding to 31) 37 of such eyes. Hinge pins pass through the openings 31 and l37 of the thus tted together eyes and yokes to releasably and pivotally connect such intermediate links. The upper ends of the pins 39 have heads which prevent downward movement of the pins and cotter keys are passed through openings in the lower portions of such pins to prevent their displacement. Each lug or eye 30 may have a stop projecting from its periphery or edge for cooperating with the adjacent link body to limit the outward pivoting of the links relative to each other. Such eyes and yokes are quite thick and heavy to have the strength required for the above-described service.

The body 29 of each intermediate link, 25A-J, has a guideway 41 which is designed to receive and mount a slip, as 42. The rear face of the guideway is sloped downwardly and inwardly, i.e., toward the axis of the pipe 23. In each of said links, grooves, 43, are provided in the side wall of the guide body and open into said guideways. Slips, as 42, are carried by each of the intermediate links, 25A-J. These links are wedge elements thicker at their top than at their bottom. These slips each operate in a guideway provided therefor. The slope of the back, 46, of each guideway is the same as the slope of the back of the slip. The biting face, 47, of each slip is thus held in a substantially vertical position (i.e., parallel to the pipe 23) regardless of the exact height of that slip relative to the link body, 29, or its radial distance from the center of the axis of the pipe, 23, the outer surface of which pipe, 23, such slip is designed to contact and thereby hold. The opposite sides of each slip have tongues as 48 that project into the grooves 43 provided at and connected to the sides of the guideways. These grooves guide the slips and hold them in proper orientation by engagement with the rear face of the guideway. Teeth 39 of the face 47 effectively grip the pipe 23 when such teeth contact the surface of such pipe.

Each of the slips are yieldably held in place by springs 49 acting on shoulder 50 in groove 51 of link body 29 on each link. The lug 52 on the slip contacts the other end of the spring. The slips are further held in place by cotter pins 54 as shown in the drawing and as described in U.S. Patent 2,301,625, page 2, right column lines 49-58.

The link assembly is provided with two handles, 55 and 69. Handle 55 has substantially the same construction as the handle 35 in the aforo-mentioned U.S. Patent 2,301,625. This handle has apertured slots 36A and 36B which lit the assembly 21 and are held in place by the pins 40A and 40B, respectively.

Handle 69 comprises a bracket 73, which tits slidably over one end of the link 25F. The bracket 73 is provided with openings 76A and 76B which register with the holes for the pin 77. Pin 77 passes through the openings corresponding to 31 and 38 in the intermediate link 25F. The head 79 on the pin 77 and a lower cotter pin, as 80, hold such pin in place.

rI`he handle 69 is formed of sturdy steel to provide for the weight and other stresses to be borne thereby. A yoke 81 is provided at the other end of the handle 69; this yoke comprises two lugs, 82 and 83, each provided with a circular eye therein, 82A and 83A, respectively. This yoke is joined by a cylindrical pin, 85, to a tongue 87 on the jack, 70. The pin 85 passes through the eyes of lugs 82 and 83 as well as eye 86 on tongue 87; this tongue slidably fits between lugs 82 and 83 and cooperates therewith to prevent twisting of the jack relative to the handle. The pin 85 joins the handle and jack so that the relative motion between the jack and the handle is limited to rotation about the longitudinal axis of the pin 85.

Shoulder 88 of the jack, further limits the clockwise rotation of the jack 70 about pin 85 and yoke 81.

The jack, 70, comprises a housing 89, a tail end lug 87 and two front lugs, 90 and 91, which form a yoke. The lugs 90 and 91 are each provided with a circular eye, 90A and 91A, respectively, for a cylindrical removable lock pin 92 provided with retainer chain 94 to housing 89. A longitudinally movable ram 93 is provided in the housing andv is actuated through a hydraulic mechanism below described by an arm 95 seated in a pivotlly movable arm housing 96. The arm 95 is removable from the housing 96. Housing 96 pivots on a fulcrum pin 97 and is pivotally attached through yoke 98 and pin 99 to a slot in the head of a pump piston 100, which pump piston seats in pump piston chamber 101.

The pump piston chamber connects via one-way valve 102 and passage 103 to ram piston chamber 105. The ram piston wall 106 forms one wall of the hydraulic uid reservoir chamber 107. A ller port 108 is provided for reservoir 107. The reservoir chamber connects via passage 103 to control valve 109. Control valve 109 alternatively provides communication either between the reservoir chamber 107-via one-way valve 110-to pump piston valve chamber 101, or valve 109 provides for communication of reservoir chamber 107 and chamber via channel 103 from the ram piston chamber. Valve 109 is controlled by handle 111. Handle 111 is provided with snap acting lock plates 112 and 113, mounted on adjustment plate 115 affixed to the pump body housing 89.

Bourdon guage 114 connects to channel 103 and provides a visual indication to the operator of the pressure in the ram cylinder. rIThis serves to notify the operator when the slips have been brought to adequate contact with the pipe 23 or other object held by the clamp 20. This also provides for indication of any decrease in pressure to notify the operator of slippage of the clamp or leakage in the hydraulic system and permits same to be promptly corrected. The lock plate 112 is shown in operative position in FIGURE l1 whereat it holds the handle 111 while lock plate 113 is therein shown in the position whereat it permits movement of the handle 111. Thereby means are provided for avoiding any accidental release of the pressure in the ram cylinder.

The valve 102 comprises a spring 120 and ball 121.

. The elongated cylindrical valve chamber 122 is provided at the radial end with a taper for a lock t of the ball therein. The longitudinal axis of this chamber is directed along a radius of a pipe 23 so that the valve will close more tightly when the pipe revolves about its longitudinal axis, and the clamp 20 is attached to said pipe shown in FIGURES 1 and 2. This relation of the valve components prevents leaking in valve 102 during protracted periods of revolution of the drill pipe. The ram piston 93 has a sealing portion 1.13 provided with conventional packing elements 116. Such packing elements are also found at 117 in the pump piston chamber 101. The upper portion of the piston 93 is threaded to permit the seating therein of the threaded portion 127 below the ram head 129. A lock nut provides for semipermanent minor adjustment of the length of the piston.

The connecting arm 71 at its lock end has locking lug 131 provided with an eye 132 which `freely tits between the interior surface of the lugs 90 and 91. The cylindrical pin 92 passes through the eyes of lugs 90 and 91 and tits into the corresponding circular eye 132 in lug 131. The above fit of the lugs limits the motion of the arm 71 relative to jack 70 to rotation about the axis of the locking pin 92. The shaft 133 of connecting arm 71 is, in the preferred embodiment, provided with a flat upper surface 135 and a flat lower surface 136. The sides, 137 and 139, of the shaft may be threaded as shown in FIGURES 4 and 5 (in lieu of the smooth cylindrical surface therefor shown in FIGURE l), and a lock nut 140 provided therefor as an extra safety feature when the clamp 20 is to be kept in a fixed clamped position on a revolving pipe, as 23, for a long interval of time. Such threads, open at their top and bottom, permit ready and complete cleaning by a brush or flushing with solvent. The clamp 20 is diagrammatically shown in FIG- URE 2 in its operative position about a vertical pipe 23, which pipe is supported by cores, as 118, in a jacket 119 therefor in a conventional `rotary table 124.

A yoke is formed by lugs, 141 and 142, at the other end of shaft 133. These lugs each lhave a cylindiical eye (143 and 145, respectively). A pivot pin, 146, cylin` drical in section, fits into said eyes. This pin 146 also passes through a circular eye of the lug of the end link 53 and so completes the connection of the link assembly 211 formed by similar intermediate links, 25A-J, end link 53, and bridging link 150. The bridging link 150 has a body 1 provided with a guideway 152 shaped as guideway 41 above described for receiving and mounting a wedge shaped slip, 153, therein. Such slip 153 is replaceable with above described wedge shaped slip element 42. Link 150 also has, at one side thereof, a lug substantially identical with the lug 30. The bridge arm 72 is firmly connected'on to the other side of said body 151 and is provided with a yoke formed of a base 1156 and two lugs, 157 and 159. The base 156 is spherically cupped at 160 to receive the hemispherical head 129 of the ram 93. The lower surface 161 of the lug 157 and the upper surface 162 of lower lug 159 are smooth and flat so as to slidably iit over surfaces 135 and 136. The bridge arm surface 163 lying adjacent shaft surface 137 is smooth and curved to i'lt such latter surface and, also, rounded at its front and rear to permit the bridge arm 72 to move smoothly over such shaft surface when in contact therewith. Thus, bridging arm 72 mechanically supports link 150 on arm 71.

The spacing of such surface 163 from the body 151 is sufficiently smallthrough use of a short base 156-so that such surface 163 does not interfere with the movement of the arm 72 while the yoke is sufficiently long to perform the function herein described for the arm 72.

The above t of the yoke of the bridging arm is directed to and provides that, in manipulation of the device during the opening and closing the group of link assemblies, as 251-7', ZSG, and 150, to the right of pin 77 as shown in FIGURE l will, while freely movable as above described, have the above-described mechanical support whereby to conveniently remain coplanar with the handle 69, jack 70, and connector arm 71. It will be noted that the locking action of the slips depends on a definite contact of the pipe surface with such slips. Such slips are held as by the springs 49 above described in their retracted positions. Unless there is a tight t provided on the pipe surface the slips will lose their holding power. When there is a large gap between slips a pipe intended to be held by a group of such slips moves toward the largest space between the slips; this results in an unequal distribution of weight on the various links and slips and a consequent jamming of the pipe on some links (usually those closest to the largest space between the links), while other links are then not functionally active. Accordingly, this invention provides a device that reduces the maximum spacing between the links. Further, during tightening of the device of this invention the stress applied to the pipe is equalized between the various links sub-assemblies, as 25A-J as well as 150 and 5-3.

It is thus seen that, according to this invention, there is provided a device that minimizes the maximum space between slips. More specifically, it reduces the space between slips as 179 and 153 to less than that of the length of the connecting means therefor. This is done, according to this invention, by a link assembly that provides oriented functioning slips, eg., 169, 154, 153, intermediate of ends of the member, 72, for connecting and disconnecting the link assembly. In a preferred embodiment such intermediate links (as 153 and ZSF) are supported by the connecting member 71. Still a further feature of this invention is the provision of the meter 114 which indicates when the slips are making adequately forceful contact with the pipe to be supported thereby. Thus the operator is able to immediately and conveniently correct his operation of the clamp, by notice of such automatic indication of adequacy of contact of slip and pipe notwithstanding the wear of the pins and slips and other parts, variations in manufacture, and skewed location of the clamp on the pipe 23 during use thereof.

According to this invention, a device is provided for quickly tightening such a link assembly for use even during the short cycles of tightening and loosening required in the replacement of drill bits in a drill string as well as for longer periods of attachment to the drill pipe.

lt is to be noted that the tension across the connection arm 71 is transmitted to pin 77 substantially directly; thereby the tension developed by the jack 70 is applied relatively evenly from pin 146 to pin 77 in a counterclockwise direction and from pin 146 to pin 77 in a clockwise direction. Further, the tension developed by the jack is also distributed relatively evenly over the slips and links, 25E, ZSG, and 15); between pin 77 and bridging arm 72. The ram piston 93 moves much more rapidly than does a screw actuated connection device for a given motion of an operator. The force applied to the links and the slips carried thereby is, however, entirely adequate to provide the force of contact needed between the slips and the pipe to prevent the motion of pipe through those slips. Additionally, such lower adequately operable pressures achieved by the device of this invention concomitant on readily controllable force of contact of the slips and pipe avoids damage to the pipe and slips and jamming `of the clamp as results from the excess forces provided by the uncontrolled slower, inconvenient tightening of a screw. The tightening provided by the device of this invention avoids stress localization due to mal-distribution of the tensile stress.

A spring 171 between bridging arm 72 and jack 70 is also provided to facilitate release of the tension of the link elements about the pipe, as 23, following opening of valve 109 to discharge hydraulic fluid from the ram piston chamber 105 to the reservoir 107 and so facilitate the disconnection of the connecting element 22.

The links, 25A-l, are each about 3 inches from center of eye 31 to center of eye 37. Variation in the diameter of the pipe 23 to be accommodated by clamp 20 of this invention is accomplished by addition or subtraction of one such link per each inch diameter change as the pins holding such links, as 39, are only removably held in place by cotter pins. A jack 70v with a 1/2 inch diameter pump portion of about l inch travel and l inch diameter ram piston with a ll/z inch travel provides, with an 18 inch long handle 95, entirely adequate force to provide the force of contact needed between pipe surface and slip surface on 81/2 inch outside diameter pipe. Bridge arm 72 and link 53 can be brought as close as desired by shortening shaft 133 and thereby more closely approximating slips 153 and 179. Thereby, according to this invention, such slips (153 and 179) are brought together so that the distance therebetween does not exceed the distance between other slips as 169 and 154.

According to this invention, the removable pin 92 (which may, if desired, be provided with a cotter pin as shown in FIGURE 2) is conveniently, permanently retained near to the jack body 89 by chain 94. Bridging arm 72 is held by spring 171 to the head 129 of ram piston 93; thus link 150 and jack 70 are arranged to be manipulated as one unit during opening and closing of the clamp 20. Thus, the assembly 20 is rapidly and conveniently made operative merely by pivoting the arm 71 about pin 146 and dropping pin 92 into the hole A provided therefor.

Opening of the clamp of this invention from its operative position is similarly quickly accomplished. Loosening of clamp 20 from its operative position (Shown in FIGURES l and 2) is accomplished merely by turning valve handle 111; tightening of clamp 20 is quickly and controllably effected by pumping handle 95.

In use of the clamp 20 of this invention, the clamp is provided with the proper number of links 25A-J for gripping the pipe 23, drill collar, or other such item. The clamp is then opened easily by removing pin 92 and wrapped about a diametral section of the pipe a convenient working distance above rotary table 124.

Links 150 and 53 are approXimated to each other, arm 72 is pivoted about the longitudinal axis of pivot pin 146, shaft 133 passes into the yoke formed by lugs 157 and 159, locking lug 131 smoothly slides between lugs 90 and 91, and locking conveniently available pin 92 is dropped into place. Clamp is then tightened and the slips thereof are then positively, conveniently and controllably brought into contact with the surface of the pipe 23, the valve 109 having been previously turned to the locking position (the position at which valve 109 connects reservoir 107 and pump piston chamber 101), by pumping handle 95 until indicator 114 indicates the pressure in ram piston chamber 105 has reached that providing a reliable, yet non-damaging grip on the pipe by the slips of the clamp. The positive engagement of the slips as 42, 169, 153, 154, 179 on the item held thereby, as pipe 23, holds the clamp thereto. If the means, as 118, purposed to grip the pipe when making up or disconnecting the drill string as above described should fail the clamp 2t) attached to pipe 23 moves downwardly therewith until it contacts the slips 113 or other part of table 124; then the slips of the clamp 20 of this invention, said clamp having been attached as above described, having been positively engaged with the pipe surface move downwardly with the walls of said pipe and are, due to the slope of the back, as 46, of the guideways, as 41, then each forced into a tighter grip on said pipe surface. 'Ihe slips, as 42, thus reliably and tirmly engage the pipe and prevent its fall further into the well. The pipe thus held by the clamp 20 of this invention is then raised for further operation by passing lifting clamps under the links, as A-I, lifting on the handles as 55 or 69, or when lifting clevises are provided in lieu of pins as 39, as is within the scope of this invention, by lifting the clamp and pipe therewith.

It is to be understood that the forms of the invention herewith shown and described are to be taken as preferred examples of the same and that various changes in shape, size and arrangement of parts may be resorted to without departing from the spirit of the invention or the scope of the subjoining claims. Having thus described tlie invention, I claim:

l. In a clamp comprising a multiplicity of like intermediate links and two end links, means for pivotally connecting the links to form a continuous assembly with the end links at the end of the assembly, means for connecting the ends of the assembly whereby the assembly may be arranged around a pipe or like object, and shiftable slips carried by each link for gripping the object,

the improvement which comprises that the means for I connecting the ends of the assembly comprises a connecting means with a rigid portion, such connecting means being pivotally attached at one of its ends to a link intermediate said end links and, at its other end, to one end link at the end of said assembly, said connecting means comprising `a tightening means, and means mechanically supporting the other end link on said rigid portion of said connecting means intermediate the ends thereof.

2. In a clamp comprising a multiplicity of like intermediate links and two end links, means for pivotally connecting the links to form a continuous assembly with the end links at the ends of the assembly, means for connecting the ends of the assembly whereby the assembly may be arranged around a pipe or like object, a shiftable gripping slip for each link, the improvement which comprises that the means for connecting the ends of the assembly comprises a pivotally connected series of elements, one of said elements being rigid and elongated, said series being attached at one end thereof to a link intermediate said end links and nearer to one end link than the other and, at its other end, to said other end link, said connecting means comprising a tightening means permanently and pivotally connected to said intermediate link, and means connected to said one end link and to said tightening means and supporting said one end link on said rigid element of said connecting means intermediate the ends thereof, whereby the slips on the end links are closer together than the ends of the means for connecting the like intermediate links said pivotal connections and means for pivotally connecting allowing rotation of all said pivotally connected elements substantially in only one plane.

3, In a clamp comprising a multiplicity of like intermediate links, two end links, means for pivotally connecting the links to form a continuous assembly with the end links at the ends of the assembly, means on the end links for connecting the ends of the assembly whereby the assembly may be arranged around a pipe or like object, and a shiftable gripping slip for each link, the improvement which comprises that the means on the end links comprise a connecting means with a rigid portion, such connecting means being pivotally attached at one of its ends to a link intermediate said end links and, at its other end to one end link at the ends of said assembly, said connecting means comprising a tightening means, said tightening means being permanently and pivotally connected to said intermediate link and being connected to indicating means, said indicating means being responsive to the force developed by said tightening means, and said rigid portion of said connecting means mechanically supporting the other end link on said connecting means intermediate the ends thereof said pivotal connections and means for pivotally connecting allowing rotation of all said pivotallyl connected elements substantially in only one plane.

4. linl a clamp comprising a multiplicity of like intermediate links and two end links pivotally connected to form an assembly adapted to be arranged around a pipe or like object, means for joining the ends of said assembly to hold the assembly around the object, at least one of said means being detachable from the link assembly, and a spring loaded slip on each link for gripping the object, the improvement which comprises that the means for joining the ends of the assembly comprises a pivotally connected series of elements, said series being attached at one end thereof to a link intermediate said end links and nearer to one end link than the other and, at its other end to said other end link, said connecting means comprising a rigid portion, said connecting means also comprising a tightening means being permanently and pivotally connected to said intermediate link, said tightening means being connected to indicating means, said indicating means being responsive to the force developed by said tightening means, and rigid bridging means connected to said one end link and to said tightening means and supporting said one end link on said rigid portion of said connecting means intermediate the ends thereof, whereby the slips on the end links are closer together than the ends of the means for connecting the like intermediate links said pivotal connections and means for pivotally connecting allowing rotation of all said pivotally connected elements substantially in only one plane.

5. A device as in claim 4 wherein, in the operating position thereof, the tightening means exerts compressive force on the bridging means towards said other end link.

6. In a clamp of the character described comprising a multiplicity of like intermediate and two end links, means for detachably pivotally connecting the links to form a continuous series assembly adapted to be engaged around objects, each link being proportioned to increase the efective diameter of the assembly a given amount whereby the clamp may be used on objects of larger and smaller diameter by increasing or decreasing the number of links in said assembly, a gripping slip shiftably vertically on each link, and movable inwardly upon downward shifting, spring means urging the slips upwardly, and means for releasably connecting the ends of the assembly to hold the slips in initial gripping engagement with the object including a member pivotally secured to one end of the assembly, the improvement which comprises that such member pivotally secured is one of a pivotally connected series of rigid connecting elements, said series being attached at one end thereof to a link intermediate said end links and nearer to one end link than the other and, at its other end to said other end link, said connecting means comprising a iiuid actuated tightening means permanently and pivotally connected to said intermediate link and operatively connected to means indicating the pressure of such Huid, and rigid bridging means connected to said one end link and to said tightening means and supporting said one end link on one of said rigid portion of said connecting means intermediate the ends thereof, whereby the slips on the end links are brought closer together than the ends of the means for connecting the like intermediate links said pivotal connections and means for pivotally connecting allowing rotation of all said pivotally connected elements substantially in only one plane.

7. A device as in claim 6 wherein in the operating position thereof the tightening means exerts compressive force on said bridging means towards said other end link.

8. A device as in claim 6 wherein said uid actuated tightening means is located in one of said pivotally connected series of rigid elements, said means comprising a housing which includes a ram piston chamber, a llluid I reservoir chamber, a pump piston chamber, and valve chambers, a movable ram in said ram piston chamber being slidably located in said ram piston chamber and one end of which ram contacts said bridging means, a valve chamber between said ram piston chamber and said pump piston chamber provided with a one-way valve permitting ow toward said ram piston chamber, said chamber being longitudinally elongated in the direction of passing from the periphery to the center of said objects about which said plurality of links are adapted to be engaged, said valve containing an inlet orifice, an orifice blocking means, and a spring, said spring urging said orice blocking means toward said oriiice in a direction away from the center of said object, whereby said valve serves to maintain operative pressure in the ram piston chamber on rotation of said device when said device is operatively connected to said object about which said plurality of links are adapted to be engaged.

References Cited in the tile of this patent UNITED STATES PATENTS 883,630 Dunn Mar. 31, 1908 1,104,579 Thorsby July 21, 1914 2,301,625 Johnson Nov. 10, 1942 2,406,607 Jensen Aug. 27, 1946 FOREIGN PATENTS 984,592 France Feb. 28, 1951 63 8,250 Great Britain June 7, 1950 

